Transcript Lecture4_210_pt1

Psychology 210
Lecture 4
Kevin R Smith
Vision
Sensory System
– The eye
– Exactly what we sense from our environment
Perceptual System
– The brain
– How we put together what we sense into a
visual picture
The brain constructs our
environment
Multiple experiences of an item
lead to different interpretations
The Visual Sensory System
Light is made of waves
Wavelength
– Different colors have different wavelengths
Amplitude
– Different amplitudes lead to differences in brightness
Visible spectrum
–
–
–
–
400nm to 750nm
ROY G BIV
Short wavelengths are near blue and violet
Long wavelengths are near red and orange
Properties of Light and Waves
The color of an object is
determined by its abilities
across two dimensions
– Absorption
– Reflection
Colors that are reflected
are the colors that we see
– A red sweater is red
because it reflects
wavelengths that we
perceive as red
Other wavelengths would
be absorbed and NOT
visible as a color for this
sweater
Properties of Light and Waves
Black is a color that
absorbs all other
colors
– ie. It is the absence of
reflected color
White is a color that
reflects all other
colors
– ie. It is the presence of
all colors
prisms
White object
Properties of Light and Waves
Refraction
– The change of
direction of the waves
Occurs in water
Different substances
refract light
differently
The eye
Sclera
– Outer covering that
protects the eye
and gives it shape
Cornea
– Protective covering for
the eye
– Begins to bend the light
waves and focus them
Aqueous humor
– Fluid filled area behind
the cornea
– Provides nutrients to
the cornea and lens
Parts of the eye
Pupil
– Area in the center of the eye
– Controls the amount of light that enters
– Iris
The muscle that controls the widening or narrowing of the pupil
Lens
– Bend to focus light onto the retina
– Accommodation
The process of the bending of the lens to properly focus the image on our
retina
Vitreous humor
– Gives the eye its shape
– Does not regenerate
The vitreous humor your born with is what you still have
– Floaters
Debris that gathers in the vitreous humor and casts shadows onto the retina
Retina
Translates light waves into an electrical signal our brain
can process
Concave
– Object on retina is translated upside-down
Photoreceptors
– Rods and cones
Optic Disk/ Optic Nerve
– Area in the retina where nerves and blood vessels exit the eye
– Forms a blind spot
Fovea
– Area in center of retina
Layers of the Retina
Four main types of
visual processing
neurons
– Ganglion cell layer
– Amacrine and
bipolar cell layer
– Horizontal cells
Visual Sensory
Neurons
– Photoreceptors
Rods
Cones
Rods and Cones
Where a sensory signal
(light waves) gets
changed into electrical
energy
– Process called transduction
Rods
– Sensitive to black and
white
– Most of them in periphery
Cones
– Sensitive to color
– Most of them in fovea
Rods
Contain rhodopsin
120 million in a
human eye
Responsible for
night vision
Very sensitive to
light
Very poor clarity
Cones
6 million in the
human eye
Responsible for
vision in bright
light
Excellent clarity
3 different types
with different
pigments
Cones
Three different types
– Blue, short
– Green, medium
– Red, long
Horizontal Cells
Integrate
information from
the
photoreceptors
Transfer that
information to
bipolar cells
Bipolar cells
Bipolar cells
Receive input from
horizontal cells and
photoreceptors
Transmit information
to amacrine cells
Contain receptive
fields
– Antagonistic centersurround organization
photoreceptors
Amacrine Cells
Horizontal cells
Amacrine Cells
Respond to changes
in the visual
environment
Connect bipolar cells,
ganglion cells, and
other amacrine cells
Ganglion cells
Receive input from bipolar and amacrine
cells
Same center-surround receptive fields
found in bipolar cells
On-center bipolar fields connect to oncenter ganglion cells
Off-center bipolar fields connect to offcenter ganglion cells
What do receptive fields do?
On-center and off-center fields provide for
greater acuity
Large unchanged surfaces don’t activate
the neurons as well as changing surfaces
with lines, cracks, and ends